Tuyeres, often mounted on a bustle pipe inject air, oxygen and fuel into blast furnaces and smelters, such as Pierce-Smith converters. Similar to tuyeres, gas injection nozzles inject oxygen and fuel into electric arc furnaces' bath of molten steel. In addition, lance nozzles inject oxygen and fuel into basic oxygen furnaces used to manufacture steel. These lances, nozzles and tuyeres are usually water-cooled and made of high conductivity copper or copper-base alloys that have minimal resistance to molten slag or metal attack. In addition to these, metallurgical vessels' lances and nozzles typically experience both hot particle erosion and molten slag or metal attack.
An additional problem is the presence of corrosive gases. These corrosive gases include acids and non-acidic reactive metal vapors. The corrosive gases, such as chlorine and sulfur dioxide often originate from fuels or the oxidation of metal sulfides in the feed stock or melt. Similar to acidic gases, reactive vapors such as, cadmium, lead, zinc, etc. typically originate from their inclusion in scrap steel feed to blast and electric arc furnaces. These gases aggressively attack metal injection devices. For example, sulfur dioxide readily reacts with copper and forms sulfides such as, copper sulfide (CuS).
Yet another problem with coated tuyeres and nozzle tips is cracking after a period of service under extreme cyclic heating and cooling. This cracking can propagate toward the inner wall, causing eventual water leakage.
Thermal barrier coatings are used in high temperature environments. The thermal barrier coating is considered a system, comprised of the superalloy substrate alloy, a metallic bondcoat and a zirconia-based outer ceramic layer. The zirconia ceramic has relatively low thermal conductivity and thus provides thermal insulation to the substrate. It would be desirable in the art to provide thermal barrier coatings that provide not only thermal insulation but also corrosive barrier protection in harsh environments such as sulfuric acid recycling furnaces.